This invention relates to the recovery of gold from ores and, more particularly, to an improved pressure oxidation process for the recovery of gold from refractory sulfidic ores.
In order to oxidize sulfide sulfur, refractory ores may be treated by pressure oxidation before leaching. If the sulfide sulfur is not substantially oxidized, leaching is inhibited and gold remains locked in the sulfides. By treating the ore in an aqueous slurry at elevated temperature and oxygen pressure, the sulfur is oxidized and removed from the ore, thereafter, the gold is readily leached with a leaching agent such as cyanide, and acceptable yields result. Thereafter the gold is readily leached and acceptable yields result.
Pressure oxidation is typically performed by passage of ore slurry through a multi-compartmented autoclave to which an oxygen-containing gas is continuously supplied. Oxygen is provided by an oxygen plant proximate the autoclave. To assure substantially complete oxidation of sulfide sulfur, excess oxygen is typically fed to an industrial scale pressure oxidation autoclave. A portion of the oxygen reacts with sulfides in the ore and a portion remains unreacted and passes through the autoclave. Because a substantial portion is not used, pressure oxidation systems have higher oxygen plant capital, maintenance and operational expenses than if the oxygen were used more efficiently.
Pressure oxidation systems typically accomplish most of the sulfide sulfur oxidation in the early stages, especially in the first compartment, of the autoclave.